The present disclosure is directed to gas turbine engines. More particularly, the disclosure relates to manufacture of disks. The disclosure relates to a process to cast a single crystal.
In manufacture of nickel-based superalloy disks (e.g., for gas turbine engine turbine sections or high pressure compressor (HPC) sections), manufacture is by forging of powder metallurgical (PM) or cast forms.
In distinction, only casting techniques are typically used to form blades, vanes, and combustor panels. Many blades are manufactured by single crystal casting techniques. In an exemplary single crystal casting technique, a seed of single crystal material is used to define a crystalline orientation that propagates into the cast blade alloy as it cools and solidifies.
In casting blades, etc., removal of high angle grain boundaries (<10°) in single crystal nickel base superalloys leads to improved creep resistance and consequently enhances its temperature capability. In addition, by properly orienting the low modulus <100> direction along the direction in which high thermal strain exists, the thermal mechanical fatigue (TMF) capability of the material can also be significantly improved.
The ring seed of single crystal material is inserted into the ceramic mold at room temperature. The assembly is heated up to casting temperatures. A thermal expansion mismatch between the seed and ceramic mold causes a gap to form between the seed and the internal core. Subsequently when molten metal is poured into the mold, the molten metal will infiltrate the gap causing extraneous grains to form and producing defects into the casting.